1. Field of the Invention
The present invention relates to a process of producing a vinyl chloride type polymer.
2. Description of the Prior Art
Conventionally, as a polymerization apparatus used for suspension polymerization of a vinyl chloride type monomer or the like, polymerization apparatuses having a polymerization vessel equipped with a reflux condenser, a heating and cooling jacket, an agitator, a nozzle through which raw materials will be charged, a nozzle through which the polymer will be taken out, etc. are known. For the purpose of dissipating the heat of polymerization, these polymerization apparatuses are provided mainly with a reflux condenser and a heating and cooling jacket. Generally, the reflux condenser is arranged at the upper part of the polymerization vessel and is for lowering the temperature of liquid contents by allowing the vapor generated in the polymerization vessel to be introduced into the reflux condenser in which the vapor is cooled with a refrigerant, such as cooling water, to condense into a liquid and allowing the condensate to flow back into the polymerization vessel. The heating and cooling jacket is arranged around the polymerization vessel and is for cooling the contents in the polymerization vessel by introducing cooling water or the like into the jacket. In particular, the reflux condenser is large in cooling capacity and attracts attention in view of an improvement in productivity or a saving in energy.
On the other hand, recently, for the purpose of improving productivity, there are attempts on that the polymerization vessel itself is large-sized and the polymerization time is shortened. However, where the polymerization time is shortened, since the quantity of the heat generated per unit time is increased, the cooling of the polymerization vessel only by the heating and cooling jacket reaches the limit, and therefore necessity results wherein the ability of heat dissipation by the reflux condenser is increased. Meanwhile, in order to repeat the polymerization with keeping the quality of the polymer obtained in each batch constant, it is required to keep the quantity of heat dissipation of each batch by the reflux condenser in good reproducibility. Generally, however, where the load of the heat dissipation of the reflux condenser is increased, the slurry foams in the polymerization vessel, which is apt to cause the slurry to flow into the reflux condenser. As a result, not only such a problem arises that polymer scale is deposited in the condenser, but also the heat dissipation ability of the reflux condenser is lowered and therefore it becomes difficult to control favorably the reproducibility of the quality of heat dissipation by the reflux condenser for each batch.
Further, in the case of a large-sized polymerization vessel, if a multiple-stage continuous operation including 100 batches or more is carried out, since deposition of scale becomes conspicuous at the part of the polymerization vessel inner wall that is in contact with the gaseous phase or at the part of the polymerization vessel inner wall near the interface between the gaseous phase and the liquid phase, such problems arise that the cooling ability of the reflux condenser is lowered and the scale mingled into the polymer degrades the quality of the resulting polymer.